Dry plate rectifier and method of producing same



Feb, 6, 194, F BRUNKE 2,189,576

DRY PLATE RECTIFIER ANDMETHOD 0F PRODUCING SAME Fired June 1o, '1937 JEL ENI/JM CARR/El? EL ECTRODE Figi 8 2 cau/WER ELECT/e005 0N0uc roe SEMI CONDUCTR 55/ COND!! C T0@ CARR/ER E/.fcreoos Inventor: F`r-itz Brmnwkne H is Attorney.

Patented Feb. 6, 1940 UNITED STATES DRY PLATE RECTIFIER AND METHOD F PRODUCING SAME Fritz Brunke, Berlin-Steglitz, Germany,

to General Electric Company,

New York assignor a corporation ol' Application June l0, 1937. Serial No. 147,577 In Germany June 22, 1936 9 Claims.

My invention relates to dry plate rectiflers, and like devices such as light-sensitive cells, wherein a semi-conductor layer composed, for example, of selenium or a selenium compound is deposited, either by a fusion processor a vaporization process, on a base or carrier electrode preferably composed of a light metal.

The object of the invention is to provide higher efficiency devices of the above type and an improved method of producing such devices.

In the manufacture of dry plate rectiiiers of the type wherein a rectifying. semi-conductor material is deposited on a carrier electrode either by a mechanical method or by exposing the carrier electrode to the vapor'of the semi-conductor material, the thickness of the resulting semiconductor layer is not maintained within deflnite limits. The vaporization method, even more than the mechanical method such as the melting of the semi-conductor material on the carrier electrode, is characterized by the occurrence of non-uniform layers and of thin portions in the layers. the layers when the rectifier is placed in operation tending to break down at these thinner portions. In order to avoid such breakdowns, the semi-conducting layer, when formed in accordance with the processes employed heretofore, must be made relatively thick. For example, in the conventional selenium rectifier having the semi-conductor layer applied to the carrier electrode by the melting process, the thickness of the semi-conducting layer is 0.1 mm. A'relatively large increase in the efiiciency of a rectifier of this type could be attained if the thickness of the semi-conductor layer could be held to a smaller value, since the resistance of the layer and the accompanying power loss would also be smaller.

In accordance with my present invention a method of depositing the semi-conductor materia] on the carrier electrode is provided whereby the thickness of the deposit is reduced, and the resulting advantage of higher efliciency, and at the same time added security against breakdown, is attained. The construction and method of operation of a rectifier incorporating rectifier cells formed in accordance with the invention will be illustrated hereinafter in connection with a rectifier of the selenium type. The invention is not, however, limited, in its application, to the selenium rectifier but may also be applied to advantage in the construction of rectifiers and like devices incorporating other semi-conductor materials for example tellurlum.

My invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring to the drawing, Figs. l, 2 and 3 are cross-sectional views of rectifier cells incorporatvthe second layer 5.

ing semi-conductor elements which have been formed on a carrier electrode in accordance with v the invention.

In Fig. 1 the rectifier cell comprises a carrier electrode I, preferably composed of a material of the group comprising the light metals, aluminum, magnesium and beryllium, a counterelectrode 2, and semi-conductor material 3 deposited on the carrier electrode I and between the latter electrode and the counter-electrode 2.

In accordance with the present invention the semi-conductor material 3 comprises two layers, a first layer 4 in contact with the carrier electrode I, and a second layer 5 between layer 4 and the counter-electrode 2. In forming the semi-conductor material 3 on the carrier electrode. the depositing of the material is preferably performed by the vaporization process. The thin layer 4, of an order of thickness preferably considerably less than 0.1 mm., preferably cornposed of selenium or a selenium compound, is first deposited on the carrier electrode by exposing the latter to the vapor of the material.

The electrode having the thin layer 4 formed thereon is maintained under pressure for several hours at a temperature between 100 C. and the melting point of selenium, or the pressure on the coated electrode may be maintained only for a short time, the temperature treatment continuing for a longer time. After the process of forming layer 4 is finished, the carrier electrode I having layer 4 thereon is exposed again to the vapor of the semi-conductor material and the secondthin layer 5, for example, of the order of 0.01 mm. in thickness, is deposited on the rst layer 4, the heat and pressure treatment being applied as before. The carrier electrode having thereon the superimposed layers 4 and 5 may then be subjected to further treatment usual in the production of an efficient rectifier.

By thus providing two superimposed layers 4 and 5 on the carrier electrode I the probability is very high that all of the thin or otherwise faulty portions in the first layer 4 will be covered by The depositing of the layers 4 and 5 has been described as being performed by the vaporization process. The invention is not limited to the use of the vaporization process however. The first layer. 4, especially, may be produced by a mechanical process, for example, by the melting of the semi-conductor on the carrier electrode. It is preferable, however, in every case to produce the second layer, 5, by the vaporization process.

I have found that the improvements in eiliciency characterizing rectiflers produced in accordance with the method of my present inven.- tion are very much greater than was to be expected only from the reduction in total thickness vof the semi-conductor material 3 deposited on the carrier electrode I. Thus I have found that in the case of rectiiiers of the selenium type formed in accordance with my present invention, not only is the current in the forward direction increased for a given voltage applied to the cell, but the leakage current, or current in the reverse direction, is also considerably reduced, as compared with the currents in the conventional selenium type rectifier. An increase of the quality factor, i. e., the ratio of forward current to reverse current, of the order of ten to twenty times, compared with the factor for the conventional selenium rectiiier was obtained. For example, the quality factor of rectiflers produced in accordance with the present invention was 60,000 at three volts, while in the case of the conventional rectifier the factor was 2,000. The cause of this surprising effect may lie in the formation of a second blocking layer between the two semiconductor layers 4 and 5. The reverse current, which is blocked by the blocking layer normally formed at the surface of the single semi-conductor layer generally employed and represented by the first layer 4, is blocked further by the second semiconductor layer 5, while this blocking layerhas no eiect on the current in the forward direction.

A still further considerable increase in the power of the rectifier can be produced if the two semi-conductor layers are made of different materials, one of the layers being of higher conductivity than the other. The effect is especially marked when the material having the better conductivity is employed for the iirst layer. Diiierent modications of the same material may he employed for the two layers. When the rectiiier is of the selenium type I have found it expedient, as illustrated in Fig. 2, to add a small quantity of iodine to the lower layer 5. the upper layer l being composed of selenium.

The invention is not limited to the provision of two semi-conductor layers of the same or different materials. As illustrated in Fig. 3, several semi-conductor layers for example, 5 and 8, may be superimposed in the same manner as shown for the two layers n Figs. 1 and 2, in order to obtain a further increase in the efficiency of the rectifier.

My invention has been described herein in particular embodiments for purposes of illustration. It is to be understood, however, that the invention is susceptible of various changes and modiiications and that by the appended claims I intend to cover any such modifications as fall within the true spirit and scope or my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is-

1. The method of producing a dry plate element having a carrier electrode, which includes melting a semi-conductor material and flowing said material over a surface of said electrode to form a semi-conductor coating thereon, and subsequently exposing said coated surface to the vapor of a semi-conductor material a plurality of times to form a plurality of semi-conductor layers superimposed on said semi-conductor coating.

2. The method of producing a dry plate element having a carrier electrode, which includes providing a plurality of semi-conductor materials ci different conductivities, exposing said electrode to the vapor of one of said semi-conductor materials until a layer of said one of said semi-conductor materials substantially less than 0.1 millimeter in thickness is formed on said electrode, said one material having the highest conductivity of said plurality of materials, and subsequently exposing said layer to the vapor of another of said semi-conductor materials until a layer of said other of said semi-conductor materials of the order of 0.01 millimeter in thickness is formed on said first-named layer.

3. The method of producing a dry plate element having a carrier electrode, which includes providing a plurality of semi-conductor materials, one of said materials having a higher conductivity than the others oi' said materials, applying to said electrode a layer of said one of said semi-conductor materials, and subsequently applying to said layer a series of superimposed layers of others of said semi-conductor materials.

4. The method of producing a dry plate element having a carrier electrode, which includes exposing said electrode to the vapor of a semiconductor material until a layer substantially less than 0.1 millimeter in thickness is formed on said electrode, and subsequently exposing said electrode having said layer thereon to the vapor of a semi-conductor material until a layer of the order of 0.01 millimeter in thickness is formed on said first-named layer.

5. A dry plate element including a carrier electrode, and a coating of semi-conductive material for said element constituted by a series oi' thin semi-conductor layers super-imposed on said electrode, the total thickness of said layers being substantially less than the required thickness of a coating of semi-conductive material for said element if said last-named coating were constituted by a single semi-conductor layer only.

6. A dry plate element including a carrier electrode, a semi-conductor layer on said electrode, and at least one semi-conductor layer superirm posed on said rst named layer, said first-named one of said layers in contact with said electrode being ci greater conductivity than the rest of said layers, the total thickness of said layers being substantially less than the required thickness ci a coating of semi-conductor material for said element if said coating were constituted by a single semi-conductor layer only.

'7. A dry plate element including a carrier electrode, a semi-conductor on said electrode composed of selenium, and a semi-conductor layer on said iirst-named layer composed of a mixture of selenium and iodine.

8. A dry plate element including a carrier electrode composed of a material of the group comprising aluminum, magnesium and beryllium and alloys of said metals, a semi-conductor layer on said electrode composed of selenium, and a semiconductor layer on said first-named layer composed of a mixture of selenium and iodine.

9. A dry plate element including a carrier electrode, a coating of semi-conductor material on said electrode including two layers, one of said layers being in contact with said electrode and of substantially less thickness than would be required for the entire coating if said entire coating were formed in a single layer only, and the second layer being in contact with said iirst layer and of such thickness that the total thickness of said first and second layers is substantially less than said required thickness of said coating if formed in a single layer.

.FRITZ BRUNKE. 

